EP2057307A2

EP2057307A2 - Process for producing nano- and mesofibres by electrospinning colloidal dispersions

Info

Publication number: EP2057307A2
Application number: EP07802732A
Authority: EP
Inventors: Michael Ishaque; Michel Pepers; Walter Heckmann; Evgueni Klimov; Andreas Greiner; Joachim H. Wendorff; Aleksandar Stoiljkovic
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2006-08-21
Filing date: 2007-08-20
Publication date: 2009-05-13
Also published as: US20100013126A1; WO2008022993A3; WO2008022993A2; JP2010501738A

Abstract

The present invention relates to a process for producing polymer fibres, especially nano- and mesofibres, by the electrospinning process, in which a colloidal dispersion of at least one essentially water-insoluble polymer and of at least one nonionic surfactant, if appropriate further comprising at least one water-soluble polymer, is electrospun in an aqueous medium. The present invention further relates to fibres obtainable by this process.

Description

Process for the preparation of nano- and mesofibres by electrospinning of colloidal dispersions

description

The present invention relates to a process for the production of polymer fibers, in particular of nano- and mesofibers, in which a colloidal dispersion of at least one essentially water-insoluble polymer is electrospun in an aqueous medium, and also fibers obtainable by this process.

For the production of nano- and mesofibers, the skilled person is familiar with a large number of methods, of which the electrospinning method (electrospinning) is of greatest importance at present, In this method, which is described, for example, by DH Reneker, HD Chun in Nanotechn. , Page 216 f., A polymer melt or a polymer solution is usually exposed to a high electric field at an edge serving as an electrode, for example, by passing the polymer melt or polymer solution under low pressure through an electric field in an electric field Due to the resulting electrostatic charging of the polymer melt or polymer solution, a material flow directed towards the counterelectrode, which solidifies on the way to the counterelectrode, is formed with this method , so-called nonwovens or ensembles of ordered fibers.

DE-A1-101 33 393 discloses a process for the production of hollow fibers with an inner diameter of 1 to 100 nm, in which a solution of a water-insoluble polymer - for example a poly-L-lactide solution in dichloromethane or a polyamide 46- Solution in pyridine - electrospun. A similar method is also known from WO-A1-01 / 09414 and DE-A1-103 55 665.

From DE-A1-196 00 162 a method for producing lawn mower wire or textile fabrics is known in which polyamide, polyester or polypropylene as a thread-forming polymer, a maleic anhydride-modified polyethylene / polypropylene rubber and one or more aging stabilizers combined, melted and together are mixed before this melt is melt-spun.

DE-A1-10 2004 009 887 relates to a process for producing fibers with a diameter of <50 μm by electrostatic spinning or spraying a melt of at least one thermoplastic polymer. The electrospinning of polymer melts allows only fibers with diameters greater than 1 μm to be produced. For a variety of applications, such as filtration applications, however, nano and / or mesofibers are required with a diameter of less than 1 micron, which can be produced by the known electrospinning process only by using polymer solutions.

However, these methods have the disadvantage that the polymers to be spun first have to be brought into solution. For water-insoluble polymers, such as polyamides, polyolefins, polyesters or polyurethanes, it is therefore necessary to use nonaqueous solvents - frequently organic solvents - which are generally toxic, combustible, irritant, explosive and / or corrosive.

In the case of water-soluble polymers, such as polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone or hydroxypropylcellulose, it is possible to dispense with the use of nonaqueous solvents. However, the fibers obtained in this way are naturally soluble in water, which is why their technical application is severely limited. For this reason, after electrospinning, these fibers must be stabilized against water by at least one further processing step, for example by chemical crosslinking, which represents a considerable technical outlay and increases the manufacturing costs of the fibers.

WO 2004/080681 A1 relates to devices and methods for the electrostatic processing of polymer formulations. The polymer formulations may be solutions, dispersions, suspensions, emulsions, mixtures thereof or polymer melts. As a method for electrostatic processing, electrospinning is mentioned, among others. In WO 2004/080681 A1, however, no concrete polymer formulations which are suitable for electrospinning are mentioned.

WO 2004/048644 A2 discloses the electrosynthesis of nanofibers and nano-composite films. For Elektroverspinnen solutions of suitable starting materials are used. According to the description, the term "solutions" also encompasses heterogeneous mixtures such as suspensions or dispersions, inter alia, fibers from electrically conductive polymers can be prepared according to WO 2004/048644 A2, which according to WO 2004/048644 A2 are preferably obtained from the corresponding monomers Get solutions.

The prior senior not previously published application "Process for the preparation of

Nano- and mesofibers by electrospinning of colloidal dispersions "of 24 February 2005 with the German application DE 10 2005 008 926.7 relates to

Process for the preparation of polymer fibers, whereby a colloidal dispersion at least one substantially water-insoluble polymer is electrospun in an aqueous medium. In this process, it has been possible for the first time to spin aqueous polymer dispersions by means of an electrospinning process, polymer fibers, in particular nano- or mesofibers, being obtained.

With the aid of the process described in DE 10 2005 008 926.7, it has been possible to avoid the above-mentioned disadvantages of the prior art and to provide a process for producing water-stable polymer fibers, in particular nanofibers and mesofibers, by the electrospinning process, in which US Pat Use of non-aqueous solvents for the preparation of a polymer solution and a post-treatment of the electro-spun fibers to stabilize the same can be dispensed with water.

The object of the present invention is to provide a process optimized for electrospinning of aqueous polymer dispersions which is optimized with respect to DE 10 2005 008 926.7, with which polymer fibers having optimized structural and / or mechanical properties can be obtained.

The object is achieved by the provision of a method in which a colloidal dispersion of at least one essentially water-insoluble polymer is electrospun in an aqueous medium.

The process according to the invention is then characterized in that the colloidal dispersion contains at least one nonionic surfactant.

With the method according to the invention fibers with a high water resistance can be obtained, which are characterized by a good mechanical stability. It is possible with the inventive method to produce nano- and mesofibers with a diameter of less than 1 .mu.m from aqueous dispersions, so that the use of non-aqueous toxic, combustible, irritating, explosive and / or corrosive solvents can be avoided. Since the fibers produced by the process according to the invention are composed of essentially water-insoluble polymers, a subsequent process step for water stabilization of the fibers is not required.

In the process according to the invention for producing the polymer fibers, a colloidal dispersion of at least one substantially water-insoluble polymer is electrospun in an aqueous medium. Substantially water-insoluble polymers are, for the purposes of the present invention, in particular polymers having a solubility in water of less than 0.1% by weight. A dispersion in the sense of the present invention, in accordance with textbook knowledge, denotes a mixture of at least two immiscible phases, one of the at least two phases being liquid. Depending on the state of matter of the second or further phase, dispersions are subdivided into aerosols, emulsions and suspensions, the second or further phase being gaseous in the case of aerosols, solid in the case of emulsions and solid in the case of suspensions. Suspensions are preferably used in the process according to the invention. The colloidal polymer dispersions preferably used according to the invention are also referred to in the technical language as latex.

In principle, the colloidal polymer dispersions according to the invention can be prepared by all processes known to the skilled person for this purpose, particularly good results being obtained by electrospinning of latexes produced by emulsion polymerization of suitable monomers. In general, the latex obtained by emulsion polymerization is used directly in the process of the invention without further workup.

The aqueous medium in which the substantially water-insoluble polymer is present is generally water. The aqueous medium may contain other additives in addition to water, eg. B. additives used in the emulsion polymerization of suitable monomers to produce a latex. Suitable additives are known in the art.

According to the invention, the colloidal dispersion used for electrospinning contains at least one nonionic surfactant.

It has been found that the addition of a nonionic surfactant to the colloidal dispersion used in the process according to the invention has a positive influence on the physical properties of the dispersion, for. As viscosity, surface tension and conductivity, the process conditions as well as the stability, and morphology of the fibers obtained, in particular nano or mesofibers has.

In principle, any surfactants known to the person skilled in the art can be used in the process according to the invention.

Without being bound by theory, it is believed that the use of nonionic surfactants provides steric stabilization of the colloidal dispersion. Thereby, the mechanical stability of the fibers obtained by the method according to the invention can be improved. Furthermore, it was found that the use of nonionic surfactants can improve the formation of fibers by electrospinning versus spraying the colloidal polymer dispersion. Furthermore, it has been found that by the presence of nonionic surfactants, a decrease in the viscosity of the colloidal dispersion can be achieved, whereby the production of thinner and more compact fibers than without addition of nonionic surfactants is possible. Furthermore, an increase in the conductivity of the dispersions and a decrease in the surface tension can be detected.

Suitable nonionic surfactants are known in the art and z. B. selected from the group consisting of (oligo) oxyalkylene groups containing surfactants, carbohydrate-containing surfactants and amine oxides.

By "(oligo) oxyalkylene" - (OR ¹ ) _n - it is to be understood that the (ON-go) oxyalkylene group-containing surfactants may have one or more oxyalkylene groups In the general formula - (OR ¹ ) _n -, R ¹ an alkylene group, preferably an alkylene group having 2 to 4 carbon atoms, and n is at least 1, preferably 3 to 30. In this case, n is usually an average of the number of oxalkylene groups. If n is greater than 1, the radicals R ¹ in the n oxyalkylene be the same or different.

Suitable (oligo) oxyalkylene-containing surfactants are, for. B. selected from the group consisting of (oligo) oxyethylene groups (polyethylene glycol groups) containing surfactants, (oligo) oxypropylene groups containing surfactants, (oligo) oxybutylene groups containing surfactants and surfactants containing two or more different oxyalkylene groups, eg. Example, (oligo) oxyethylene groups and (oligo) oxypropyl lengruppen, in random order or in the form of blocks (Blockcopolymeri- sat), z. B. block copolymers based on propylene oxide and ethylene oxide. The (oligo) oxyalkylene-containing surfactants are preferably selected from the group consisting of fatty alcohol alkoxylates, alkoxylated triglycerides and alkylalkylene glycol ethers alkylated on both sides. Suitable alkoxylates or alkoxylated compounds are, for. Ethoxylates, propoxylates, butoxylates or random or block copolymers (or oligomers) composed of two or more different alkoxylates, e.g. As ethoxylates and propoxylates.

Suitable carbohydrate-containing surfactants are, for. B. selected from the group consisting of alkylpolyglycosides, sucrose esters, Sorbinanestern (sorbitan), z. As polyoxyethylene sorbitan trioleate, and fatty acid N-methylglucamiden (fatty acid glucamides). As is evident from the aforementioned group of surfactants, the nonionic surfactants suitable according to the invention may contain either (oligo) oxyalkylene groups or carbohydrate groups or both (oligo) oxyalkylene groups and carbohydrate groups.

Suitable amine oxides are, in particular, alkyldimethylamine oxides.

It is possible to use individual surfactants or mixtures of two or more surfactants in the process according to the invention.

The abovementioned nonionic surfactants are known to the person skilled in the art and are commercially available or can be prepared by processes known to the person skilled in the art.

The nonionic surfactants used according to the invention may in principle be present in amounts in the colloidal dispersions which do not lead to coagulation. The optimum amounts are dependent, inter alia, on the surfactant used and the application temperature. The at least one nonionic surfactant is preferably present in the colloidal dispersions in an amount of from 0.5 to 10% by weight, particularly preferably from 0.3 to 5% by weight, based on the total weight of the essentially water-insoluble polymer used. It has been found that particularly good process results - both in terms of the formation of polymer fibers and in terms of quality, z. As the mechanical stability, the polymer fibers - are obtained when 0.3 to 1 wt .-%, preferably 0.5 to 1 wt .-%, based on the total weight of the dispersion, of the nonionic surfactant, z. B. a block copolymer based on various alkylene oxides, eg. B. based on propylene oxide and ethylene oxide.

The at least one nonionic surfactant contained in the colloidal dispersions according to the process according to the invention can either be prepared during the preparation of the colloidal dispersions, in particular a polymer latex which is prepared by emulsion polymerization, or subsequently after the preparation of the colloidal dispersions, for. To the finished latex prepared by emulsion polymerization. In a preferred embodiment of the present invention, the at least one nonionic surfactant is added subsequently to the final colloidal dispersion prior to the start of the electrospinning process.

According to a preferred embodiment of the present invention, in the method according to the invention is a colloidal aqueous dispersion of a

Poly (p-xylylene); polyvinylidene halides; Polyesters such as polyethylene terephthalates, polybutylene terephthalate; polyethers; Polyolefins such as polyethylene, polypropylene, poly (ethylene / propylene) (EPDM); polycarbonates; polyurethanes; natural polymers, e.g. Gum; polycarboxylic acids; polysulfonic; sulfated polysaccharides; polylactides; polyglycosides; polyamides; Homopolymers and copolymers of aromatic vinyl compounds such as poly (alkyl) styrenes, for example polystyrenes, poly-α-methylstyrenes; polyacrylonitriles; Polymethacrylnitrilen; polyacrylamides; polyimides; polyphenylenes; polysilanes; polysiloxanes; polybenzimidazoles; polybenzobisbenzazoles; polyoxazoles; polysulfides; polyesteramides; Polyarylenvinylenen; polyether ketones; polyurethanes; polysulfones; inorganic-organic hybrid polymers as ORMO- CE ^® s of the Fraunhofer Society for the Promotion of Applied Research. V. Munich; silicones; wholly aromatic copolyesters; acrylates of poly (alkyl); Poly (alkyl) methacrylates; Polyhydroxyethylmethacrylaten; polyvinyl acetates; Polyisoprene, synthetic rubbers such as chlorobutadiene rubbers, eg. B. Neoprene ^® from DuPont, nitrile-butadiene rubbers, z. Buna ^N® ; polybutadiene; Polytetrafluoroethylene; modified and unmodified celluloses, homo- and copolymers of α-olefins and copolymers composed of two or more of the above-mentioned polymer-forming monomer units existing selected group of water-insoluble polymer. All the abovementioned polymers can be used in the latices to be used according to the invention individually or in any combination with one another and in any desired mixing ratio.

In particular with homopolymers or copolymers based essentially on acrylates, aromatic vinyl compounds such as styrenes, alpha-methylstyrenes; Vinylacetates, vinyl ethers, butadienes, isoprenes, methacrylates, acrylamide, vinylsulfonic acid, vinylsulfonic acid esters, vinyl esters, vinyl alcohol, acrylonitrile, vinyl sulfones and / or vinyl halides, good results are achieved.

In a particularly preferred embodiment of the present invention, the substantially water-insoluble polymers are selected from homo- or copolymers based essentially on aromatic vinyl compounds such as styrenes, alpha-methylstyrenes, acrylates, eg. As methyl or butyl acrylates, and / or methacrylates.

All of the aforementioned polymers can be used uncrosslinked or crosslinked, provided that their solubility in water is less than 0.1% by weight.

The aforementioned substantially water-insoluble polymers are commercially available or can be prepared according to processes known to those skilled in the art. In a preferred embodiment of the present invention, substantially water-insoluble polymers are used, which are prepared by emulsion polymerization, suitable by emulsion polymerization available polymers are mentioned above. The polymer latex obtained in the emulsion polymerization can be used directly in the electrospinning process according to the invention as a colloidal dispersion, preferably after addition of the nonionic surfactant.

Particularly good results are obtained with colloidal polymer suspensions, the average weight-average particle diameter of the at least one essentially water-insoluble polymer generally being from 1 nm to 2.5 μm, preferably from 10 nm to 1.2 μm, particularly preferably from 15 nm to 1 μm is. The average weight-average particle diameter of emulsion-produced latex particles which are used in a preferred embodiment in the method according to the invention is generally from 30 nm to 2.5 microns, preferably from 50 nm to 1, 2 microns (determined according to W. Scholtan and H. Lange in Kolloid Z. and Polymers 250 (1972), pp. 782-796 by means of ultracentrifuge). Very particular preference is given to using colloidal polymer suspensions, in particular latexes, in which the polymer particles have a weight-average particle diameter of 50 nm to 500 nm, in particular very particularly preferably 50 nm to 250 nm.

The colloidal suspension preferably used according to the invention may have particles with monomodal particle size distribution of the polymer particles or with bimodal or polymodal particle size distribution. The terms mono-, bi- and polymodal particle size distribution are known to the person skilled in the art.

If the latex to be used according to the invention is based on two or more monomers, the latex particles can be arranged in any manner known to the person skilled in the art. For example, only particles with gradient structure, core-shell structure, salami structure, multi-core structure, multi-layer structure and raspberry morphology may be mentioned.

The term latex also means the mixture of two or more latices. The preparation of the mixture can be carried out by any known method, e.g. by mixing two latices at any time prior to spinning.

According to a further preferred embodiment of the present invention, in addition to the at least one water-insoluble polymer and the at least one nonionic surfactant, the colloidal dispersion additionally contains at least one water-soluble polymer, a polymer having a solubility in water of at least 0 being water-soluble for the purposes of the present invention, 1 wt .-% is understood. Without being bound by theory, the at least one water-soluble polymer which is preferably additionally present in the colloidal dispersions can serve as a template polymer. With the help of the template polymer, the fiber formation from the colloidal polymer dispersion (electrospinning) is further favored over spraying (electrospraying). The template polymer serves as a kind of "glue" for the essentially water-insoluble polymers of the colloidal dispersion.

After the preparation of the polymer fibers according to the method of the invention, the water-soluble polymer in a preferred embodiment of the method according to the invention, for. B. removed by washing / extraction with water.

After removal of the water-soluble polymers, water-insoluble polymer fibers, in particular nano- and microfibers, are obtained, without disintegration of the polymer fibers.

The water-soluble polymer may be a homopolymer, copolymer, block polymer, graft copolymer, star polymer, hyperbranched polymer, dendrimer, or a mixture of two or more of the foregoing types of polymers. According to the findings of the present invention, the addition of at least one water-soluble polymer not only accelerates / promotes fiber formation. Rather, the quality of the resulting fibers is significantly improved.

In principle, all of the water-soluble polymers known to those skilled in the art may be added to the colloidal dispersion of at least one substantially water-insoluble polymer in an aqueous medium, in particular with polyvinyl alcohol; Polyalkylene oxides, eg. For example, polyethylene oxides; Poly-N-vinylpyrrolidone; hydroxymethylcelluloses; hydroxyethylcelluloses; hydroxypropyl; Carboxymethylcelluloses; maleic; alginates; collagens; Combinations composed of two or more of the monomeric units constituting the above-mentioned polymers, copolymers composed of two or more monomer units constituting the aforementioned polymers, graft copolymers composed of two or more of the monomeric units constituting the aforementioned polymers, star polymers composed of two or more of them above-mentioned polymer-forming monomer units, highly branched polymers composed of two or more of the above-mentioned polymer-forming monomer units and dendrimers composed of two or more of the above-mentioned polymer-forming monomer units selected group of selected water-soluble polymers particularly good results. In a preferred embodiment of the present invention, the water-soluble polymer is selected from polyvinyl alcohol, polyethylene oxides and poly-N-vinylpyrrolidone.

The abovementioned water-soluble polymers are commercially available or can be prepared according to processes known to those skilled in the art.

Regardless of the embodiment, the solids content of the colloidal dispersion to be used according to the invention-based on the total weight of the dispersion-is preferably from 5 to 60% by weight, particularly preferably from 10 to 50% by weight and very particularly preferably from 10 to 40% by weight. %.

In the further embodiment of the present invention, the colloidal dispersion to be used in the process according to the invention comprises at least one substantially water-insoluble polymer, at least one nonionic surfactant and optionally at least one water-soluble polymer in an aqueous medium, based on the total weight of the dispersion, from 0 to 25 wt .-%, particularly preferably 0.5 to 20 wt .-% and most preferably 1 to 15 wt .-%, of at least one water-soluble polymer.

Thus, in a preferred embodiment, the colloidal dispersions used according to the invention comprise, in each case based on the total amount of the colloidal dispersion,

i) 5 to 60 wt .-%, preferably 10 to 50 wt .-%, particularly preferably 10 to 40

% By weight of at least one substantially water-insoluble polymer, ii) from 0.1 to 10% by weight, preferably from 0.3 to 5% by weight, particularly preferably from 0.3 to 1

% By weight of at least one nonionic surfactant iii) 0 to 25% by weight, preferably 0.5 to 20% by weight, more preferably 1 to 15% by weight of at least one water-soluble polymer, and iv) 5 to 94, 9 wt .-%, preferably 10 to 89.2 wt .-%, particularly preferably 15 to 88.5 wt .-% water.

The weight ratio of substantially water-insoluble polymer to the water-soluble polymer preferably present in the colloidal dispersion depends on the polymers used. For example, the substantially water-insoluble polymer and the preferably used water-soluble polymer can be used in a weight ratio of 10: 1 to 1:10, preferably 9: 1 to 1: 9, particularly preferably 8: 2 to 2: 8. The colloidal dispersion to be used in accordance with the invention can be electrospun in any manner known to the person skilled in the art, for example by extrusion of the dispersion, preferably of the latex, under low pressure through a cannula connected to one pole of a voltage source to a counter electrode arranged at a distance from the cannula outlet. Preferably, the distance between the cannula and the counterelectrode acting as collector and the voltage between the electrodes is set such that between the electrodes an electric field of preferably 0.5 to 2 kV / cm, particularly preferably 0.75 to 1.5 kV / cm and most preferably 0.8 to 1 kV / cm forms.

In particular, good results are obtained when the inner diameter of the cannula is 50 to 500 μm.

It has been found that the stability and compactness of the fibers produced by the process according to the invention can be further improved if the fibers - preferably after removal of the water-soluble polymer - heated to a temperature above the glass transition temperature or the melting point of the polymer or polymer mixture used become. The temperature is dependent on the glass transition temperature or the melting point of at least one water-insoluble polymer and is z. B. 5 to 50 ⁰ C, preferably 10 to 40 ⁰ C, particularly preferably 15 to 30 ⁰ C above the glass transition temperature or the melting point of the respective at least one water-insoluble polymer. Usually, for a period of z. B. 5 to 90 min., Preferably 10 to 60 min., Preferably in a low oxygen or oxygen-free atmosphere, eg. B. under nitrogen or under argon heated.

Depending on the intended use of the fibers produced, it may be expedient to subsequently chemically bond them together or, for example. through a chemical intermediary to network with each other. As a result, for example, the stability of a fiber layer formed by the fibers can be further improved, in particular with regard to water and temperature resistance.

Another object of the present invention are fibers, in particular nano- and mesofibers, which are obtainable by the method according to the invention. The fibers according to the invention are distinguished by the fact that, owing to the addition according to the invention of the at least one nonionic surfactant, they have optimized structural and / or mechanical properties compared to fibers which are produced without addition of the nonionic surfactant, in particular with regard to uniformity, compactness and Stability. The diameter of the fibers according to the invention is preferably 10 nm to 50 μm, particularly preferably 50 nm to 2 μm and very particularly preferably 100 nm to 1 μm. The length of the fibers depends on the purpose and is usually 50 microns to several kilometers.

Not only compact fibers, but in particular hollow fibers, in particular those having an inner diameter of less than 1 μm and particularly preferably of less than 100 nm, can be produced by the process according to the invention. For producing such hollow fibers, the fiber produced by the above-mentioned method of the present invention may be coated with, for example, a substance selected from the group consisting of inorganic compounds, polymers and metals, and then the water-insoluble polymer contained therein, for example, thermally, chemically, biologically, radiation-induced, photochemically Plasma, ultrasound or extraction with a solvent, be degraded. The materials suitable for coating and the methods suitable for dissolving the fiber-internal material are described, for example, in DE-A1-101 33 393.

Furthermore, the present invention relates to colloidal dispersions of at least one substantially water-insoluble polymer in an aqueous medium, which additionally comprises at least 0.5% by weight of a water-soluble polymer having a solubility in water of at least 0.1% by weight and at least one nonionic Containing surfactant.

In a preferred embodiment, the colloidal dispersions according to the invention, based in each case on the total weight of the dispersion, contain i) 5 to 60% by weight, preferably 10 to 50% by weight, more preferably 10 to 40

% By weight of at least one substantially water-insoluble polymer, ii) from 0.1 to 10% by weight, preferably from 0.3 to 5% by weight, particularly preferably from 0.3 to 1% by weight of at least one nonionic surfactant iii ) 0 to 25 wt .-%, preferably 0.5 to 20 wt .-%, particularly preferably 1 to 15

Wt .-% of at least one water-soluble polymer, and iv) 5 to 94.9 wt .-%, preferably 10 to 89.2 wt .-%, particularly preferably 15 to 88.5 wt .-% water.

Suitable substantially water-insoluble polymers, aqueous media, water-soluble polymers and nonionic surfactants and suitable amounts of these components in the colloidal dispersions are mentioned above. The colloidal dispersions according to the invention are preferably used in the process according to the invention. Furthermore, the present invention relates to the use of nonionic surfactants in a process for producing polymer fibers by an electrospinning process.

A preferred electrospinning process and suitable surfactants are mentioned above.

By using the nonionic surfactants in the electrospinning process, on the one hand, an improvement of the electrospinning process with respect to a

Favoring fiber formation (electrospinning) over spraying of the colloidal dispersion preferably used in the electrospinning process. Furthermore, the structural and mechanical properties of the polymer fibers produced according to the electrospinning process can be improved, in particular with regard to the fiber quality uniformity and stability and the

Spinnability of the fibers.

Other objects, features, advantages and applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features alone or in any combination form the subject matter of the invention, regardless of their combination in the claims or their dependency.

Show it:

1 shows a schematic representation of a device suitable for carrying out the electrospinning method according to the invention,

2 is a scanning electron micrograph of the fibers obtained according to Example 2 before and after water treatment,

Fig. 3 scanning electron micrograph of the fibers obtained according to Example 3, heated to 1 10 ⁰ C, before and after

Water treatment

Fig. 4 scanning electron micrograph of the obtained according to Example 3 fibers, heated to 130 ⁰ C, before and after

Water treatment.

1, suitable for carrying out the method according to the invention for electrospinning comprises a syringe 3 provided at its tip with a capillary nozzle 2 connected to one pole of a voltage source 1 for receiving the colloidal dispersion 4 according to the invention. Opposite the outlet of the capillary nozzle 2, a square counterelectrode 5 connected to the other pole of the voltage source 1 is arranged at a distance of about 20 cm, which acts as a collector for the fibers formed.

During operation of the device, a voltage between 18 kV and 35 kV is set at the electrodes 2, 5 and the colloidal dispersion 4 is discharged through the capillary nozzle 2 of the syringe 3 at a low pressure. Due to the electrostatic charging of the essentially water-insoluble polymers in the colloidal dispersion due to the strong electric field of 0.9 to 2 kV / cm, a material flow directed towards the counterelectrode 5 occurs, forming fiber 6 on the way to the counter electrode 5 solidified, as a result of which fibers 7 with diameters in the micrometer and nanometer range are deposited on the counter electrode 5.

According to the invention, a colloidal dispersion of at least one essentially water-insoluble polymer and at least one nonionic surfactant is electrospun in an aqueous medium using the aforementioned device.

The determination of the solids content in the dispersion is determined gravimetrically by means of a Mettler Toledo HR73 Halogen Moisture Analyzer by approximately 1 ml of sample is heated within 2 minutes at 200 ⁰ C and the sample dried to constant weight, and then weighed.

The average particle size is the weight average value d ₅₀ , determined by means of an analytical ultracentrifuge (according to W. Scholtan and H. Lange in Kolloid-Z and Polymers 250 (1972), pp. 782-796).

The size, i. the diameter and length of the fibers is determined by evaluation of electron micrographs.

1. Preparation of colloidal dispersions

1.1 General rule

The polymer latex used in the following examples contains polystyrene in an amount of. 40 wt .-%, based on the total weight of the polymer latex. The mean particle size (weight average, d ₅₀ ) is 100 nm (Example 1, 2) or 200 nm (Example 3). The preparation of polymer latices containing polystyrene having the abovementioned particle sizes is carried out by customary methods known to the person skilled in the art. In this case, usually a polymer latex is obtained with a polystyrene content of> 30 wt .-%, which is then diluted with water to the desired concentration.

As the water-soluble polymer is poly is used (vinyl alcohol) (PVA I) having a weight average molecular weight _(Mw) of 195000 g / mol, which is hydrolyzed to 98% (MOWIOL ^® 56-98 from Kuraray Specialties Europe KSE GmbH), or PO - ly (vinyl alcohol) (PVA II) with a weight average molecular weight (Mw) of 145000 g / mol, which is 99% hydrolyzed (MOWIOL ^® 28 - 99 from Kuraray Specialties Europe KSE).

As the nonionic surfactant is a block copolymer based on propylene oxide and ethylene oxide (Basensol ^® of BASF AG).

The preparation of the electrospinning according to Example 2 used colloidal dispersions is carried out by mixing a polystyrene-containing latex with water, wherein the above-mentioned polymer latex containing polystyrene in an amount of. 40 wt .-%, based on the total weight of the polymer latex, is obtained. The solids content of the dispersion to be spun is 18% by weight. To the polymer latex is added the above-mentioned polyvinyl alcohol in aqueous solution (10% strength by weight), so that the colloidal dispersion to be spun contains about 4.5% by weight PVA II and the weight ratio of polystyrene to polyvinyl alcohol (PVA II ) in the mixture is 80:20. The nonionic surfactant is added to this mixture, the amount of nonionic surfactant in the colloidal dispersion to be spun being about 0.5% by weight.

In a comparative experiment, a corresponding colloidal dispersion is spun without addition of a nonionic surfactant.

1.2 example dispersions

Table 1 summarizes the colloidal dispersions to be spun:

1) comparative 2) PS = polystyrene having an average particle size of 100 nm (in water about 40 wt .-% strength) 3) based on the total weight of the dispersion 4) aqueous solution 5) addition amount of water added 6) Basensol ^®: block copolymer based on propylene oxide and ethylene oxide from BASF AG

2. electrospinning the dispersions produced

The colloidal dispersions I and I V prepared according to item 1 are electrospun in the apparatus shown in FIG.

The dispersion is thereby conveyed at a temperature of 15 to 16 ⁰ C by a syringe 3 with a provided at the top capillary nozzle 2 with an inner diameter of 0.3 mm with a sample feed of 0.7 ml / h, wherein the distance between the electrodes 2, 5 is 200 mm and a voltage of 30 kV is applied between the electrodes. The resulting fibers are treated with water for 17 hours at room temperature to remove the water-soluble polymer.

FIG. 2 shows the scanning electron micrographs of the fibers produced from the colloidal dispersions I (left) and IV (right). The upper images each show the fibers obtained before treatment with water, and the lower figures show the corresponding fibers after treatment with water. In FIG. 2,

I: fibers by electrospinning the dispersion I; I V fibers by electrospinning the dispersion I V.

As can be seen from FIG. 2, the addition of nonionic surfactant gives more uniform polymer fibers than without the addition of surfactant, which do not dissolve in water in individual polystyrene particles.

3. Heating of polymer fibers produced according to the invention to temperatures above the glass transition temperature

3.1 Dispersions and conditions of electrospinning used:

It is a colloidal dispersion is used, which is based on a 40 wt .-% polystyrene latex. The weight-average particle size of the polystyrene particles (d ₅₀ ) is 200 nm. The dispersion contains 4.5% by weight, based on the total amount of dispersion, of polyvinyl alcohol PVA II, the weight ratio of polystyrene to PVA II being 85:15, and 0 , 8 wt .-%, based on the total amount of the dispersion, of the nonionic surfactant.

Table 2 below summarizes the components of the colloidal dispersion to be spun and their amounts:

1) PS = polystyrene having an average particle size of 200 nm (in water 40 wt .-% ig) 2) based on the total weight of the dispersion 3) aqueous solution ⁴⁾ Basensol ^®: block copolymer based on propylene oxide and ethylene oxide from BASF AG

The electrospinning is carried out in the apparatus shown in Figure 1, under the following conditions: Inner diameter of the capillary nozzle: 0.3 mm

Sample feed: 0.7 ml / h

Distance of the electrodes 2, 5: 200 mm voltage between the electrodes: 10 kV.

The resulting fibers are treated with water for 17 hours at room temperature to remove the water-soluble polymer.

A portion of the fibers obtained after the electrospinning is heated before treatment with water at temperatures of 1 10 ⁰ C and 130 ⁰ C in each case for 15, 30 and 60 minutes. The other part of the resulting fibers is heated after treatment with water under the appropriate conditions.

FIGS. 3 and 4 show scanning electron micrographs of the respective fibers in comparison to unheated fibers. Photographs of fibers that were not treated with water prior to heating are shown on the left, and images of fibers treated with water before heating are shown on the right. 3 shows photographs of fibers are shown, which were heated at 1 10 ⁰ C, and in Figure 4 photographs of fibers are shown, which were heated at 130 ⁰ C. Further, in Figure 3, for comparison, a fiber is shown (before and after water treatment) which has not been heated.

In FIG. 3,

V without heating

In each of Figures 3 and 4,

A heating for 15 minutes at 1 10 ⁰ C (Figure 3) and 130 ⁰ C (Figure 4) B heating for 30 minutes at 110 ⁰ C (Figure 3) and 130 ⁰ C (4) C heating for 60 minutes to 110 ^° C. (FIG. 3) or 130 ^° C. (FIG. 4)

It can clearly be seen on the pictures in FIGS. 3 and 4 that the heating can achieve a smoothing of the fibers.

The invention is not limited to one of the above-described embodiments, but can be modified in many ways. It can be seen, however, that the present invention relates to a process for the production of polymer fibers, in particular of

Nanofibers and mesofibres, after the electrospinning process, in which a colloidal dispersion at least one substantially water-insoluble polymer (and at least one nonionic surfactant) optionally further comprising at least one water-soluble polymer in an aqueous medium is electrospun. Furthermore, the present invention relates to fibers obtainable by this process.

All features and advantages arising from the claims, the description and the drawing, including constructive details, spatial arrangements and method steps, can be essential to the invention, both individually and in the most varied combinations.

LIST OF REFERENCE NUMBERS

1 voltage source

2 capillary nozzle

3 syringe

4 colloidal dispersion

5 counter electrode

6 fiber formation

7 fiber mat

Claims

claims

1. A process for the preparation of polymer fibers, wherein a colloidal dispersion of at least one substantially water-insoluble polymer is electrospun in an aqueous medium, characterized in that the colloidal dispersion contains at least one nonionic surfactant.

2. The method according to claim 1, characterized in that the at least one nonionic surfactant is selected from the group consisting of (ON go) oxyalkylene groups containing surfactants, carbohydrate groups containing surfactants and amine oxides.

3. The method according to claim 1 or 2, characterized in that the at least one nonionic surfactant in an amount of 0.1 to 10 wt .-%, preferably 0.3 to 5 wt .-%, particularly preferably 0.3 to 1 Wt .-%, most preferably 0.5 to 1 wt .-%, based on the total weight of the dispersion, is used.

4. The method according to any one of claims 1 to 3, characterized in that the at least one substantially water-insoluble polymer has a solubility in water of less than 0.1 wt .-%.

5. The method according to any one of claims 1 to 4, characterized in that the at least one substantially water-insoluble polymer of the poly (p-xylylene); polyvinylidene halides; polyesters; polyethers; polyolefins; Polycarbonates; polyurethanes; natural polymers; polycarboxylic acids; Polysulfonic acids; sulfated polysaccharides; polylactides; polyglycosides; Polyamides; Homopolymers and copolymers of aromatic vinyl compounds; Polyacrylonitriles; Polymethacrylnitrilen; polyacrylamides; polyimides; polyphenylenes; polysilanes; polysiloxanes; polybenzimidazoles; polybenzobisbenzazoles; Polyoxazoles; polysulfides; polyesteramides; Polyarylenvinylenen; polyether ketones; polyurethanes; polysulfones; inorganic-organic hybrid polymers; Silicones; wholly aromatic copolyesters; acrylates of poly (alkyl); Poly (alkyl) methacrylates; Polyhydroxyethylmethacrylaten; polyvinyl acetates; polyisoprene; synthetic rubbers; polybutadiene; polytetrafluoroethylene; modified and unmodified celluloses; Homo- and copolymers of α-olefins; Copolymers composed of two or more of the above-mentioned polymers forming monomer units and combinations thereof is selected from the group.

6. The method according to claim 5, characterized in that the at least one essentially water-insoluble polymer is a homopolymer or copolymer based essentially on acrylates, aromatic vinyl compounds such as styrene and alpha-methylstyrenes, vinyl acetates, vinyl ethers, butadienes, isoprenes, Methacrylates, acrylamide, vinylsulfonic acid, vinylsulfonic acid esters, vinyl esters, vinyl alcohol, acrylonitrile, vinylsulfones and / or vinyl halides.

7. The method according to any one of claims 1 to 6, characterized in that the average weight-average particle diameter of the at least one substantially water-insoluble polymer is between 1 nm and 2.5 microns.

8. The method according to any one of claims 1 to 7, characterized in that the colloidal dispersion additionally contains at least one water-soluble polymer having a solubility in water of at least 0.1 wt .-%.

9. The method according to claim 8, characterized in that the water-soluble polymer is selected from the group consisting of homopolymers, copolymers, graft copolymers, star polymers, highly branched polymers and dendrimers.

10. The method according to claim 8 or 9, characterized in that the water-soluble polymer of the polyvinyl alcohol, polyalkylene oxides, poly-N-vinylpyrrolidone, hydroxymethylcelluloses, hydroxyethylcelluloses, Hydroxyprop- pylcellulosen, carboxymethylcelluloses, maleic acids, alginates, collagen, combinations of two or more the above-mentioned polymers forming monomer units, copolymers composed of two or more of the above-mentioned polymer forming monomer units, graft copolymers composed of two or more monomer units forming the above polymers, star polymers composed of two or more monomer units forming the above-mentioned polymers, hyperbranched Polymers composed of two or more monomeric units and dendrimers constituting the above-mentioned polymers composed of two or more monomer units constituting the above-mentioned polymers

Group is selected.

1 1. A method according to any one of claims 1 to 10, characterized in that the solids content of the colloidal dispersion, based on the total weight of the dispersion, 5 to 60 wt .-%, preferably 10 to 50 wt .-%, particularly preferably 10 to 40 wt .-% is.

12. The method according to any one of claims 1 to 1 1, characterized in that the colloidal dispersion, based on the total weight of the dispersion, 0 to 25 wt .-%, preferably 0.5 to 20 wt .-% and particularly preferably 1 to Contains 15 wt .-% of a water-soluble polymer.

13. The method according to any one of claims 1 to 12, characterized in that the fibers obtained after electrospinning are heated to a temperature above the glass transition temperature or the melting point of the employed at least one substantially water-insoluble polymer.

14. Fiber obtainable by a process according to one of claims 1 to 13.

15. Fiber according to claim 14, characterized in that it has a diameter of 10 nm to 50 microns, preferably from 50 nm to 2 microns and more preferably from 100 nm to 1 micron.

16. Fiber according to claim 14 or 15, characterized in that it has a length of at least 50 μm.

17. Colloidal dispersion of at least one substantially water-insoluble polymer in an aqueous medium further comprising at least 0.5% by weight, based on the total weight of the dispersion, of a water-soluble polymer having a solubility in water of at least 0.1% by weight. -% and at least one nonionic surfactant.

18. Use of nonionic surfactants in a process for producing polymer fibers by an electrospinning process.